Method of making acrylic bicomponent yarn or fabric with latent crimp development



y 1 1967 YOSHIMASA FUJITA ETAL 3,

METHOD OF MAKING ACRYLIC BI'COMPONENT YARN OR FABRIC WITH LATENT CRIMP DEVELOPMENT Filed July 2, 1963 IN VENTORS. YOSH/MA SA FUJ/TA KAZ UM KE/ 74/?0 SH/MODA KOJ/ M/YASH/TA ATTORNEY 3,33,8fi5 Patented July 11, 1967 fine 3,330,895 METHOD OF MAKiNG ACRYLIC BICOMPG- NENT YARN R FABRIC WITH LATENT CRllviP DEVELOPMENT Yoshimasa Fujita, Kazumi Nakagawa, Keitaro Shimoda,

and Koji Miyashita, Saidaiji, Japan, assignors to American Cyanamid Company, Stamford, Conn, a corporation of Maine Filed July 2, 1963, Ser. No. 292,391 Claims priority, application Japan, July 12, 1962, 37/29,292 Claims. (Cl. 264-103) This invention relates to a method for making bulky yarns and fabrics of synthetic acrylic fibers, said bulky yarns and fabrics being stable under hot, humid conditions.

At present, the conventional process for making a bulky yarn or fabric of acrylic fibers involves the blending together of acrylic fibers of two types having two different properties; (a) a first type of fiber which exhibits high shrinkage upon the application of heat and (b) a second type of fiber which exhibits low shrinkage upon the application of heat. The yarns and fabrics made from such a blend of fibers spun together are heat treated so as to permit the high-shrinkage fibers to shrink. However, such a process has a serious drawback in that when the yarn is heat treated with hot water or steam to produce a bulk therein, and/or the yarn is subjected to heat in dyeing and other operations, it tends to become slim as it is flattened or the bulk is lost. Also, during handling and heating, such as in laundering of the fabrics, the yarn therein tends to become slim losing bulk.

It is an object of the present invention to provide a process for making bulky yarns and fabrics having an attractive appearance and free of the tendency to become slim during subsequent treatments at elevated temperatures, such as in dyeing and laundering.

We have found that the above object may be accomplished by making such yarns or fabrics from multi-component fibers of two dissimilar acrylonitrile polymeric components eccentrically disposed towards each other in distinct zones extending throughout the length of said fibers with adjoining surfaces in intimate adhering contact. These components have a difference in thermal shrinkage as spun fibers which, upon heat treatment of the resulting fibers, causes these fibers to produce a good bulk by the formation of three-dimensional coil crimps. However, when heat treated at temperatures sufficiently elevated to produce a satisfactory bulkiness in the resulting yarns or fabrics, it was found that these fibers could not satisfactorily be processed on conventional textile handling equipment, such as the conventional spinning equipment.

It is another object of this invention to provide a process for the formation of yarns and fabrics of multi-component fibers utilizing conventional spinning equipment.

With the conventional spinning equipment, it is not only difiicult to carry out the spinning of crimpless fibers (as is well known), but an excessive crimp also makes spinning extremely difficult. This is particularly true of multi-component fibers, for when such fibers are manufactured by a process including a high temperature heat treatment to which conventional acrylic fibers are subjected, a number of coil crimps occur in the fibers. As these fibers are then spun, they are liable to creep round the cylinder of the card, and ultimately, the spinning operation must be suspended.

As will be described in further detail in this specification, we have successfully solved this problem by initially inhibiting the occurrence of too many coil crimps during the manufacture of multi-component fibers by selecting compositions for the two components of such fibers having appropriate rates of shrinkage at various temperatures and by controlling the temperature at which such fibers are heat treated during the manufacture thereof to preclude full development of the crimp and then allowing the crimps to fully develop in such fibers in the course of a subsequent heat treatment conducted after forming the multi-component fibers into yarns or fabrics.

It is still another object of the present invention to provide a process for the manufacture of a high quality multi-component fiber which does not give rise to too many coil crimps during its manufacture but which does give rise to a substantially larger number of such crimps upon heat treatment at elevated temperature after forming into yarns or fabrics, wherein such fibers also possess properties desirable for use in textile products.

For a clearer and more detailed description of this invention and its relationship to the previously known process for preparing bulky yarns and fabrics, reference may be made to the subjoined description and the accompanying drawing wherein:

FIGURE 1 is a cross-sectional view of a bundle of multi-component fibers such as may be utilized in the practice of this invention;

FIGURE 2 is a schematic representation of the prior art type of bulky yarn utilizing a blend of high-shrink fibers and low-shrink fibers; and

FIGURE 3 is a schematic representation of a bulky yarn in accordance with the present invention.

The multi-component fibers employed in the practice of the present invention are each composed of two dissimilar acrylonitrile polymeric components eccentrically disposed towards each other in distinct zones extending throughout the length of such fibers with the adjoining surfaces in intimate adhering contact. Preferably, the fibers have cross sections about as illustrated in FIGURE 1, wherein the dotted zone represents one component and the undotted zone represents the other component. These multi-component fibers are formed by concurrently spinning the two dissimilar acrylic polymer components into fibers by extrusion, coagulation, drawing, and heattreatrnent steps. The extrusion and coagulation steps are performed by apparatus now known to those skilled in the art. Examples of such apparatus are to be found in Kulp et al., US. Patent No. 2,386,173, issued Oct. 2, 1945; Calhoun, US. Patent No. 3,006,028, issued Oct. 31, 1961; and Fujita et al., US. application Ser. No. 208,- 884, filed July 10, 1962, and assigned to the assignee of the present application, now US. Patent No. 3,182,106, issued May 4, 1965.

The two components which make up the multi-component fibers may be selected from acrylonitrile polymers, copolymers, and graft-copolymers, as well as mixtures thereof each containing at least about by weight of acrylonitrile. As will be described in more detail hereinafter, the difference in thermal shrinkage of the components is controlled by incorporating into any such polymer one or more additional ingredients.

Representative compounds which may be polymerized with acrylonitrile to form acrylonitrile polymerization products useful for the practice of this invention are compounds containing a single CH =C grouping, for instance, the vinyl esters and especially the vinyl esters of saturated aliphatic monocarboxylic acids, e.g., vinyl acetate, vinyl propionate, vinyl butyrate, etc., vinyl and vinylidene halides, e.g., the vinyl and vinylidene chlorides, bromides and fluorides; allyl-type alcohols, e.g., allyl alcohol, methallyl alcohol, ethallyl alcohol, etc.; allyl, methallyl and other unsaturated monohydric alcohol esters of monobasic acids, e.g., allyl and methallyl acetates, laurates, cyanides, etc.; unsaturated carboxylic acids (e.g., acrylic, itaconic, and alkacrylic acids, e.g., methacrylic, ethacrylic, etc.) and esters and amides of such acids (e.-g., methyl, ethyl, propyl, butyl, etc., acrylates and methacrylates, acrylamide, methacrylamide, N- methyl, ethyl, -propyl, -butyl, etc., acrylamides and methacrylamides, etc.); methacrylonitrile, ethacrylonitrile and other hydrocarbon-substituted acrylonitriles; unsaturated aliphatic hydrocarbons containing a single CH =CH grouping, e.g., isobutylene, etc.; and numerous other vinyl, acrylic and other compounds containing a single CH =CH grouping which are copolymerizable with acrylonitrile to yield thermoplastic copolymers. Alkyl esters of alpha, beta-unsaturated polycarboxylic acids may also be copolymerized with acrylonitrile to form copolymers, e.g., the dimethyl, ethyl, -propyl, -butyl, etc, esters of maleic, fumaric, citraconic, etc., acids.

It is further possible to incorporate into said polymer other compounds containing the vinyl group, such as a vinylpyridine or an unsaturated sulfonic acid having polymeric ethylene bonds.

Vinylpyridines which can be employed in making copolymers with acrylonitrile, and used as herein described, are vinylpyridines represented by the formula C H: C Hg and which include Z-Vinylpyridine, 3-vinylpyridine and 4-vinylpyridine; methyl vinylpyridines represented by the formula (II) CH=CH and which include 2-methyl-3-vinylpyridine, 3-vinyl-4- methylpyridine, 3-vinyl-S-methylpyridine, 2-vinyl-3-methylpyridine, 2-vinyl-4-methylpyridine, 2-vinyl 5 methylpyridine, 2-vinyl-6-methylpyridine, 2 methyl 4 vinylpyridine and 3-methyl-4-vinylpyridine. The vinylpyridines embraced by Formula II are a preferred subgroup within a broader class of vinylpyridines that are advantageously employed in making copolymers which, in filamentary form, are used in practicing the present invention and which may be represented by the formula (III) C H: G H:

and wherein R represents a lower alkyl radical, more particularly a methyl, ethyl, propyl (including n-propyl and isopropyl) or butyl (including n-butyl, isobutyl, sec.- butyl and tert.-butyl) radical. Other examples include 2-vinyl-4,6-dimethylpyridine, the 2-'and 4-vinylquinolines, 2-vinyl-4,6-diethylpyridine and others embraced by the formula CH=CII2 if, of 50,000 to 100,000, e.g., about 70,000S0,000, as calculated from a viscosity measurement of the said polymerization product in dimethyl formamide using the Standinger equation (reference: Houtz US. Patent No. 2,404,713, dated July 23, 1946).

To be suitable for the practice of this invention, the two components forming the multicomponent filament ordinarily should have a difierence in thermal shrinkage as spun fibers of less than about 4% at C. and at least about 5.5% at C. in order that during the performance of the process of this invention, a relatively small number of crimps may be developed prior to forming the resulting fibers into a yarn or fabric and a substantially larger number of crimps may be developed by a subsequent heat treatment of the yarn or fabric at a more elevated temperature. These two dissimilar acrylonitrile polymeric components may differ from each other in having different monomers copolymerized with acrylonitrile or in having the same monomers copolymerized in different proportions with acrylonitrile so as to provide the proper difference in thermal shrinkage. The critical criterion is that the two components must provide a multi-component fiber which does not give rise to more than about 5 coil crimps per 25 mm. at a temperature sufiiciently high to satisfactorily heat treat the fiber after drawing but which does give rise to at least about 10 coil crimps per 25 mm. upon being heat treated after such fibers are formed into yarns or fabrics. This critical requirement results from the difficulty in processing or spinning equipment coil crimped fibers having more than about 5 coil crimps per 25 mm. and from the fact that less than about 10 coil crimps per 25 mm. does not provide sufficient bulkiness in the final product.

The characteristic of coil crimp in a multi-component fiber depends upon the difierence in composition and thermal shrinkage of the two components comprising such a fiber, the temperature at which such fiber is heat treated, and the denier of the fiber. The degree of thermal shrinkage of the two components comprising a multi-component fiber may be controlled by controlling the proportion of ingredients to be contained in each component, i.e., acrylonitrile and other monomers copolymerized therewith, examples of which have been given above. Generally speaking, the rates of shrinkage of the two components generally increase with increase in the proportion of other vinyl compounds copolymerized with the acrylonitrile. Additionally, the amount of shrinkage of the two components increases with increase in temperature at which the fiber is heat treated. Thus, it is readily possible to select pairs of components which have a differential thermal shrinkage of less than a certain amount at one temperature and a greater amount of thermal shrinkage at a more elevated temperature.

The number of coil crimps produced on heat treatment of such a multi-component fiber is a function of the difference in the thermal shrinkage of the components comprising such fiber as well as the denier of such fiber. For a given size fiber, the higher the difference in thermal shrinkage achieved by the fiber, the larger the number of coil crimps per unit of length that will be produced. Thus, the selection of a pair of components having less than a certain difference in thermal shrinkage at a first temperature and greater than a higher difference of thermal shrinkage at a more elevated temperature permits the production of fibers having relatively few coil crimps by heat treating them below such certain temperature and permits the subsequent increase in the number of coil crimps by the later heat treatment at a temperature above the more elevated temperature.

Tables 1 and 2 show the coil crimp characteristics of multi-component filaments which are made up of copolymers containing 90% acrylonitrile and 10% methyl acrylate (Recipe A), 92% acrylonitrile and 8% methyl acrylate (Recipe B), and 93% acrylonitrile and 7% methyl acrylate (Recipe C), respectively.

NOTE .1he d" in the above table denotes the denier of each multicoinponent filament.

TABLE 2 Rates of shrinkage Numbers of coil crimps (per 25 mm.) Temperature of heattreatment, 0. Recipe B, Recipe A, A-B,

percent percent per- 2d 3d 6d d cent It will be apparent from the foregoing tables, that with respect to these copolymer filaments, the difference in the rate of shrinkage upon heat treatment at 100 C. is less' than about 4% and that the difference in the rate of shrinkage upon heat treatment at 115 C. or more is greater than about 5.5%. It also will be noted that, in general, for any given temperature of heat treatment, a higher denier filament acquires fewer coil crirnps per 25 mm. and that more coil crimps per 25 mm. are developed in any fiber of a given denier the higher the temperature of the heat treatment.

In the known processes for the manufacture of fibers from acrylonitrile polymers, it is considered essential that such fibers be heat treated in a relaxed state subsequent to drying and orientation and the minim-um treating temperature for such process is in excess of 105 C. Such relaxation is described in US. Patent No. 2,883,260, issued April 21, 1959 and US. Patent No. 2,614,289, issued October 21, 1952.

In the process for producing multi-component fibers according to the present invention, just as in the process for producing the conventional mono-component acrylic fibers, the aforementioned heat treatment in a relaxed state is an essential part of the process. The trouble is, however, that 'if a multi-co-mponent filament is heat treated at sufficiently elevated temperatures (e.g., over 100 C.) too many coil crirnps occur'in the fibers in this early stage of the process. Such a fiber having excessive three-dimensional coil crirnps has various drawbacks,

such as the tendency toward creeping round the card, which tendency makes spinning'the fibers into threads practically impossible.

We have found an interesting relationship between the heat treatment temperature and the soil crimping characteristics of the two components comprising a multicomponent fiber due to the difference in their rates of shrinkage as illustrated in Tables 1 and 2 above. Based on this finding, we have devised a method for producing bulky yarns and fabrics which comprises selecting the compositions of the two acrylonitrile polymer components such that the diffeernce in shrinkage between them is at least about 5.5% at 115 C. so as to provide for adequate numbers of coil crirnps in the final product but is less than about 4% at 100 C. The process involves inhibiting the occurrence of excessive numbers of coil crirnps during the manufacture of the fibers by maintaining the treating temperatures at all stages of the process subsequent to spinning and drawing and prior to carding (and particularly the temperature at which the fiber is heat treated in a relaxed state) below about C. so as to facilitate the carding of such fibers. Subse quent to such carding operation, the textile product is heat treated at a temperature over C. thereby producing a sufficient number of coil crirnps to give a good bulk to the fibers and, at the same time, improve the overall physical properties of these fibers,

While it is true that the higher the temperature at which this final heat-treatment is conducted, the greater the number of coil crirnps that are produced in the fiber and, therefore, the greater the bulkiness, the preferred range is 115 C. to about C. since excessively higher temperatures might degrade the fibers or tend to cause yellowish discoloration thereof. This heat treatment can be conducted under either hot-dry or hot-wet conditions, such as by the use of heated air or other gases, superheated steam, saturated steam at supcratmospheric pressure, boiling water under superatmospheric pressure, heated non-aqueous liquids, etc.

FIGURES 2 and 3 show schematic views, respectively, of a bulky conventional yarn and a bulky yarn made according to the present invention. As illustrated schematically in FIGURE 2, the conventional bulky yarn is composed of two different kinds of fibers; (a) high shrinking fibers, represented by the heavier lines, which tend to constitute the core of the yarn and (b) low shrinking fibers, shown as fine lines, which tend to constitute the sheath of the yarn. Since the low shrinking fibers tend to migrate to the outside of the yarn bundle during the bulking operation, they are liable to get loose from the bulky yarn during subsequent handling. Additionally, this yarn tends to become slim in the course of various subsequent processings to which textile products may be subjected, such as the heat treatment to produce the bulkiness, dyeing, laundering, and other heating processes, and and degree of slimness progresses as such processes are repeated.

In contrast, as schematically illustrated in FIGURE 3, the bulky yarn of this invention is made from a plurality of multi-component fibers, all of which form coil crirnps. Since all of the fibers behave in the same fashion, there is no tendency for any of the fibers to migrate from the core toward the surface of a yarn bundle. Also, the large number of coil crirnps produced serves to so intertwine each fiber with its adjacent fibers that it is extremely diificult for any fibers to get loose from the bulloy yarn. For these reasons, the bulky yarn produced in accordance with this invention is additionally characterized by the uniform density of fibers throughout the yarn and, more important, by the high stability of this bulkiness during subsequent heat treatments because the coil crirnps are not eliminated by heat treatments, whether dry-heat or wet-heat is used. Thus, the bulky yarn of this invention, once made bulky, would not become slim no matter how often heating is repeated, Therefore, this yarn possesses a high degree of solidity throughout, so that it can withstand repeated dyeings and launderings.

Another advantage of this invention is that, whereas the conventional bulky yarn suffers a loss of yarn strength during manufacture when the bulk is produced therein, the bulky yarn of the present invention shows an increase in yarn strength upon being subjected to a treatment to produce the bulk in the yarn.

EXAMPLE 1 A spinning solution of a copolymer composed of 90% acrylonitrile and 10% methyl acrylate in a concentrated aqueous solution of sodium thiocyanate was extruded into an 8% aqueous solution of sodium thiocyanate. The tow thus obtained was washed in water, drawn in boiling water to 800% the initial length, and dried in air at a dry-bulb temperature of 105 C. and a wet-bulb temperature of 70 C. until the filaments contained less than 3% of moisture. The dried filaments were treated in a relaxed state for 10 minutes in saturated water vapor at 120 C., followed by mechanical crimping, oil treatment, cutting, and drying to produce a regular yarn (A) of 3 denier. Another tow made under conditions similar to the above was drawn 130% between hot plates at 120 C. and cut to prepare an after-drawn yarn (B).

On the other hand, a copolymer composed of 90% acrylonitrile and 10% methyl acrylate, and another copolymer composed of 95% acrylonitrile and methyl acrylate, respectively, were dissolved in a concentrated aqueous solution of sodium t-hiocyanate to prepare two different spinning solutions. Equal amounts of the two solutions were simultaneously extruded into an 8% aqueous solution of sodium thiocyanate by means of an apparatus similar to the one disclosed in U.S. patent application Serial No. 208,884, filed July 10, 1962, which is fure nished with two metering pumps. The filaments thus prepared were washed with water, and drawn in boiling water to 800% the initial length.

The spinnerette contained 500 orifices each of which measured 0.08 millimeter in diameter. The filaments were then dried in a highly humid atmosphere, i.e. at a drybulb temperature of 100 C. and a wet-bulb temperature of 70 C., so that the filaments contained less than 3% of moisture. The filaments were further treated in a relaxed state for minutes in boiling water, followed by mechanical crimping, oil treatment, and cutting to produce a multi-component fiber staple (C).

A bulky yarn was produced by spinning together A and B in a proportion of 50:50 and, then, treating the resulting yarn in saturated water vapor at 120 C. for 5 minutes.

On the other hand, a bulky yarn was manufactured by spinning the multi-component fibers into yarn and treating it in saturated water vapor at 120 C. for 5 minutes.

The strength and elongation properties of the abovementioned two bulky yarns before and after the highbulk treatments in saturated water vapor at 120 C. are shown in the following table.

While the bulky yarn produced from the blend of A and B showed slimness at various points, the bulky yarn made from C was full-bodied and had a superior hand owing to the coil crimps produced therein.

EXAMPLE 2 Following the procedure of Example 1, regular fibers (D) of 3 denier and after-drawn fibers (E) of 5 denier were manufactured from a copolymer containing 90% acrylonitrile, 9.25 methyl acrylate, and 0.75% methallylsulfonic acid.

On the other hand copolymers composed of 90% acrylonitrile, 9.25% methyl acrylate, and 0.75% methallylsulfonic acid, and 94% acrylonitrile, 4.5% methyl acrylate and 1.5% methallylsulfonic acid, respectively, were separately dissolved.

Equal amounts of the spinning solutions were extruded by means of a multi-component spinning apparatus furnished with two metering pumps, and multicomponent fibers (F) of 3 denier were manufactured in the same manner as described with reference to the multi-component fibers of Example 1.

Q A bulky yarn was manufactured by mix-spinning D and E in a proportion of 40:60 and, then, treating the spun fibers in boiling water to produce a bulk therein.

Another bulky yarn was manufactured by treating the 5 spun fibers F in saturated water vapor at 125 C. for 5 minutes to give three-dimensional coil crimps to the fibers.

The results of a comparative dyeing test which was carried out with the bulky yarn made from D and E and 10 the bulky yarn F in a boiling dye bath containing a cationic dyestuff showed that whereas the former yarn gave rise to various slim points, the latter was found to be a full-bodied bulky yarn completely free from local slimness.

EXAMPLE 3 Just as in Example 1, regular fibers (G) of 3 denier and after-drawn fibers (H) of 3 denier were manufactured from a copolymer composed of 85% acrylonitrile, 8% vinyl acetate, and 7% vinylpyridine. On the other hand, a copolymer composed of 85% acrylonitrile, 8%

vinyl acetate, and 7% vinylpyridine and another copolymer comprising 90% acrylonitrile, 5% vinyl acetate and 5% vinylpyridine were independently dissolved.

Equal amounts of the spinning solutions thus prepared were extruded concurrently with an apparatus similar to the one used in Example 1 which was equipped with two metering pumps. Thus, in the same manner as Example 1, multi-component fibers (I) of 3 denier were produced.

A bulky yarn was manufactured by mix-spinning fibers G and H in a proportion of 50:50 and, then, treating them in boiling water to produce bulkiness. On the other hand, another bulky yarn was manufactured by treating fibers I in saturated water vapor at 115 C. for 5 minutes. Whereas the bulky yarn composed of fibers G and H showed local slimness, the bulky yarn of multicomponent fibers was full-bodied and did not become slim when subsequently dyed.

We claim:

1. A process for making bulky yarns and fabrics of crimped multi-component fibers of two dissimilar acrylonitrile polymeric components eccentrically disposed towards each other in distinct zones extending throughout the length of said fibers with adjoining surfaces in intimate adhering contact, said components being selected to have a difference in thermal shrinkage as spun fibers of less than about 4% at 100 C. and at least about 5.5% at 115 C.; said process comprising concurrently spinning said two dissimilar acrylonitrile polymer components into fibers by extrusion, coagulation, drawing, and heat-treatment steps, all of such heat-treatment steps subsequent to the last drawing step being conducted at temperatures below about 100 C., forming the resulting fibers into yarn or fabric, and, finally, heat-treating the yarn or fabric at a temperature above about 115 C. to develop the bulk therein by substantially increasing the crimps therein.

2. A process as defined in claim 1 wherein said heattreatment steps applied to said multi-component fibers include relaxation subsequent to the last drawing step, said relaxation step being conducted at elevated temperatures below about 100 C.

3. A process as defined in claim 2 wherein said relaxation is performed in boiling water.

4. A process as defined in claim 1 wherein said forming of the resulting fibers into yarn or fabric includes mechanically crimping said fibers, forming said fibers into staple, and spinning said staple into yarn prior to the final heattreatment of the final yarn or fabric.

5. A process for making bulky yarns and fabrics of crimped multi-component fibers of two dissimilar acrylonitrile polymeric components eccentrically disposed towards each other in distinct zones extending throughout the length of said fibers with adjoining surfaces in intimate adhering contact, said components being selected Cal to have a difference in thermal shrinkage as spun fibers of less than about 4% at 100 C. and at least about 5.5% at 115 C.; said process comprising concurrently spinning said two dissimilar acrylonitrile polymer components into fibers by extrusion, coagulation, drawing, and heattreatment steps, all of said heat-treatment steps subsequent to the last drawing step being conducted at temperatures below that at which about 5 coil crimps per 25 millimeters are developed, forming the resulting fibers into yarn or fabric, and, finally, heat-treating the yarn or fabric at a temperature above that at which about 10 coil crimps per 25 millimeters are developed to develop the bulk therein by substantially increasing the crimps there- References Cited UNITED STATES PATENTS 10 ALEXANDER H. BRODMERKEL, Primary Examiner.

F. S. WHISENHUNT, A. KOEOKERT,

Assistant Examiners. 

1. A PROCESS FOR MAKING BULKY YARNS AND FABRICS OF CRIMPED MULTI-COMPONENT FIBERS OF TWO DISSIMILAR ACRYLONITRILE POLYMERIC COMPONENTS ECCENTRICALLY DISPOSED TOWARDS EACH OTHER IN DISTINCT ZONES EXTENDING THROUGHOUT THE LENGTH OF SAID FIBERS WITH ADJOINING SURFACES IN INTIMATE ADHERING CONTACT, SAID COMPONENTS BEING SELECTED TO HAVE A DIFFERENCE IN THERMAL SHRINKAGE AS SPUN FIBERS OF LESS THAN ABOUT 4% AT 100*C. AND AT LEAST ABOUT 5.5% AT 115*C.; SAID PROCESS COMPRISING CONCURRENTLY SPINNING SAID TWO DISSIMILAR ACRYLONITRILE POLYMER COMPONENTS INTO FIBERS BY EXTRUSION, COAGULATION, DRAWING, AND HEAT-TREATMENT STEPS, ALL OF SUCH HEAT-TREATMENT STEPS SUBSEQUENT TO THE LAST DRAWING STEP BEING CONDUCTED AT TEMPERATURES BELOW ABOUT 100*C., FORMING THE RESULTING FIBERS INTO YARN OR FABRIC, AND, FINALLY, HEAT-TREATING THE YARN OR FABRIC AT A TEMPERATURE ABOVE ABOUT 115*C. TO DEVELOP THE BULK THEREIN BY SUBSTANTIALLY INCREASING THE CRIMPS THEREIN. 